1. Field of the Invention
This invention relates to a safety glass composed of a layer of glass and a layer of a plastic used, for example, as an automobile windshield or a windowpane of a building, and to a laminated structure useful for it.
2. Description of the Prior Art
A safety glass (laminated glass) composed of a three layer structure of glass-plastic-glass has previously been used in applications requiring safety, for example as an automobile windshield glass The plastic layer in this structure is provided for the purpose of preventing scattering of glass fragments and penetration of a colliding object in the event of glass shattering. When, for example, a human body collides with this laminated structure, the shattered glass fragments will not scatter, but rather it is impossible to prevent laceration by sharp glass fragments
In recent years, attempts have been made to provide a further plastic layer for prevention of laceration on an indoor side of the three layer structure. This structure is composed of four layers of glass-plastic-glass-plastic. If the outermost plastic layer on the indoor side is composed of a material having penetration resistance and being capable of preventing glass scattering and laceration, a two-layer structure composed of glass and plastic will suffice
The following two techniques have previously been proposed in regard to a windshield of this two-layer structure.
Japanese Patent Publication No. 27050/1982 discloses a structure composed of glass, an impact absorbing layer of a plastic material (mainly polyurethane) on it, and a protective layer thereon composed of a partially crosslinked aliphatic polyurethane.
Japanese Laid-Open Patent Publication No. 51339/1986 describes a laminated structure produced by successively laminating (a) an impact-absorbing layer of 0.3 to 2.0 mm in thickness of polyurethane or polyvinyl butyral as a main component, and (b) a layer with a thickness of 50 to 200 micrometers of a polyester as a main component on a glass sheet.
The structure described in the above-cited Japanese Patent Publication has the following problems. The partially-crosslinked polyurethane layer as the outermost layer on the indoor side does not have sufficient chemical resistance, soiling resistance and laceration resistance. Since it is a crosslinked structure, its flexibity is greatly reduced. Injuring at the time of stuffing, etc. may be prevented to some extent since it has rubbery elasticity, but after repeated rubbing, this polyurethane layer is susceptible to injury. The crosslinking density of the surface having rubbery elasticity cannot be increased to such an extent that penetration of chemicals such as organic solvents or soiling is prevented. Yellowing due to contact of a tobacco smoke or swelling owing to label application on such a surface cannot be prevented, and the structure has a short service life.
The laminate described in Japanese Laid-Open Patent Publication No. 51339/1986 does not substantially have sufficient resistance to laceration.
Generally, a biaxially stretched polyester film is widely used as a transparent material or the like because it has superior mechanical properties and transparency. But it has poor abrasion resistance and is susceptible to injury on the surface. In order to remove these defects, it was proposed to coat the film with a thermosetting resin.
For example, Japanese Patent Publication No. 53703/1985 discloses a scratch-resistant laminate obtained by applying a primer layer of a polyester resin on an article of polyethylene terephthalate, coating a top coat paint comprising a vinyl polymer containing a melamine group-containing (meth)acrylate as a main ingredient.
Japanese Patent Publication No. 43303/1985 discloses an abrasion-resistant laminate obtained by applying a resin composition comprising a vinyl pyrrolidone/acrylate copolymer and a quaternary ammonium salt polymer as a primer layer to a polyester polymer, then coating on it a top coat paint composed of colloidal silica and a hydrolyzate of an alkoxysilane having an epoxy group, and curing the top coat paint.
The laminated structure disclosed in Japanese Patent Publication No. 53703/1985 does not have a fully satisfactory hardness In the laminated structure disclosed in Japanese Patent Publication No. 43303/1985, the hardness and adhesion of the top coat layer tend to be reduced upon immersion in boiling water.